This invention relates generally to electrical medical leads and, in particular, to cardiac stimulation leads.
In the field of cardiac pacing, there are available pacemakers designed to provide stimulus pulses to and sense the electrical activity of a patient's heart. Typically, leads intended for use in the ventricle employ an essentially straight lead body which allows location of the electrode at the ventricular apex. However, in those applications where the electrode is desired to be located in other areas of the heart, such as the atrium for A-V sequential pacing or the ventricular septum for his bundle monitoring, it is desirable to use a lead which is provided with a curve in its distal portion to direct the electrode to its desired location within the heart. For example, atrial pacing leads may display a J-shaped bend over their distal portion to enable placement of the tip electrode in the atrial appendage of the right atrium, or an L-shaped bend to facilitate placement of the electrode in the coronary sinus.
There have been two general approaches to providing a lead with a desired bend or curve. The most common approach has been to fabricate the lead in such a manner that it tends to assume the desired curve, straightening the lead for insertion by means of a stiffening stylet. In these leads, the curve facilitates the location of the electrode at the desired location. Examples of such leads are discussed in U.S. Pat. No. 3,939,843 issued to Smyth, and U.S. Pat. No. 3,729,008 issued to Berkovits and U.S. Pat. No. 4,332,359 issued to McCorkle. The preset curve of the lead may be also straightened by means of a tubular structure such as a needle or a catheter, as described in U.S. Pat. No. 3,516,412 issued to Ackerman and U.S. Pat. No. 3,866,615 issued to Hewson. As an alternative to providing the lead with a preset curve, some leads are adapted to be used with stylets which temporarily impart a desired curve to the lead. Examples of this technique can be found in U.S. Pat. No. 4,136,703 issued to Wittkampf and in commonly assigned U.S. patent application Ser. No. 306,050 by Williams for a "Positive Anchoring A-V Lead."